Insighting the interaction mechanism of zirconium xerogel coagulants with humic acid: the protective effect of acetylacetone

The use of efficient modification methods determines the wide application potential of zirconium salt coagulants. In this study, zirconium xerogel coagulants were prepared by acetylacetone regulation, and they exhibited application potential in a wider range of pH (pH = 5–9) and higher coagulation performance (residual turbidity < 2 NTU) than ZrCl4 and PAC at a dosage of 0.2 mM. In addition, the acetylacetone-regulated xerogel coagulants were insensitive to changes in organic matter and were effective in removing turbidity even at high organic matter concentrations. The interaction mechanism between the zirconium xerogel coagulants and humic acid involving a complexation effect in the acidic environment and a sweeping effect in the alkaline environment has been proposed. The interpretation of this mechanism further revealed the “protective umbrella effect” of acetylacetone, which might work as a hydrolysis inhibitor to reduce the hydrolysis rate, as a chelating ligand to control the release of H+, and as a barrier to prevent organic matter from coming into direct contact with metal ions. These characteristics provide better stability, a higher effluent pH and higher turbidity removal. This study outlines the interaction mechanism of zirconium xerogel coagulants with humic acid and provides evidence for the contribution of acetylacetone in fabricating efficient gel coagulants.